It is well known that the implementation of fire doors within buildings and other structures provides a means for restricting and/or retarding the spread of fire from one area to another in the event such a catastrophe occurs. Previously known fire doors have typically relied upon mechanical stepping ratchets and/or cams to allow the fire door to drop to secure the opening. However, such prior art structures have been given to failure, and have been found to occasionally jam or otherwise cease working. To avoid this problem, the prior art has suggested the implementation of friction discs, operating as clutch discs or the like, to provide a means for retarding the rate at which the fire door drops or closes. However, this type of structure has been found to be quite sensitive to adjustments, with the friction discs operating in a fluid bath which is not given to adjustability to accommodate various rates of closure. Additionally, such structure is complex in structure and operation, and expensive to manufacture.
It is most desirable that overhead fire doors include mechanisms for controlling the rate of closure for the purpose of providing safety to inhabitants of the building who might otherwise be pinned beneath a rapidly closing door, and to further prevent damage or buckling to the door itself which would inhibit its utility. However, for the reasons presented above the prior art is incapable of efficiently and effectively controlling such closure rate, and is itself given to failure in operation and extensive costs in manufacture.